1. Field of the Invention
The present invention relates to an ink-jet head back-up device and an ink-jet printer.
In an ink-jet printer, ink is sprayed from thin nozzles of an ink-jet head and thereby characters and so forth are printed on a recording medium such as a sheet of paper. In this arrangement, the following problems occur. Ink in the nozzles can become dry and have an increased viscosity. Paper dust can be adhered onto and cover the nozzles because the nozzles are wet due to the ink. Due to vibration, bubbles enter the ink-jet head via the nozzles. Due to these problems, some or all the nozzles clog and ink spray failure occurs. Further, the pressure by which ink is sprayed is absorbed by the bubbles and insufficient spraying is performed. Thus, printing quality is substantially degraded. Further, in an operation where the ink cartridge is replaced with a new old one, air enters the nozzle. When the air entered the nozzles, ink jet failure occurs. In order for the nozzle to provide stable ink jet printing, the ink-jet printer include an ink-jet head back-up device.
The ink-jet head back-up device absorbs forcibly ink from the nozzles. Thereby, high-viscosity ink, bubbles, paper dust and so forth are removed from the ink-jet head. Thus, the ink-jet head back-up device is a sort of head projection mechanism which performs an unclogging operation on a nozzle (hereinafter, simply referred to as a `purge`). This purge is performed after ink cartridge replacement is performed. In other cases, the purge is performed if necessary or periodically. For example, the purge is during an initial operation immediately after the ink-jet printer power-on operation or when an operator gives an instruction.
2. Description of the Related Art
An ink-jet head back-up device in the related art includes a pump which is connected with a tube from a nozzle cap which covers the nozzles of an ink-jet head, a valve and so forth. In order to miniaturize the ink-jet head back-up device, the valve is included in the pump. The valve is operated by the pressure in the pump or the operation of the pump. Thus, the valve is indirectly operated.
The purge includes, generally speaking, a main purge and an emptying purge. In the main purge, in a condition where the nozzle cap covers the nozzles of the ink-jet head, the pump and valve operate with a predetermined timing. Thereby, first, absorption is performed and ink and bubbles in the nozzles of the ink-jet head are absorbed into the pump. Then, the ink and bubbles are discharged from the pump. In the emptying purge, in a condition where the nozzle cap is removed from the ink-jet head, the above-mentioned operations are performed. Thereby, ink adhered in the nozzle cap and the tube is removed.
As mentioned above, the valve is operated by the pressure in the pump or the operation of the pump. Thus, the valve is indirectly operated. Accordingly, valve closing timing is slightly delayed. Thereby, although instantaneously, ink flows in the reverse direction to the nozzle cap and the purge cannot be properly performed. Thus, the ink-jet head back-up device in the related art has a reliability problem.